Refactor screen/monitor so that gfx::Screen returns monitor object.

ui/gfx/screen_android.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/gfx/screen.h"
 
 #include "base/logging.h"
+#include "ui/gfx/monitor.h"
 
 namespace gfx {
 
 // static
-gfx::Size Screen::GetPrimaryMonitorSize() {
+const gfx::Monitor* Screen::GetPrimaryMonitor() {
+  static SimpleMonitor* monitor = new SimpleMonitor();
   NOTIMPLEMENTED() << "crbug.com/117839 tracks implementation";
-  return gfx::Size(1, 1);
+  return monitor;
 }
 
 // static
 int Screen::GetNumMonitors() {
   return 1;
 }
 
 }  // namespace gfx